Field of the Invention
The present invention relates to an aircraft generating device for driving an electric generator coupled with an aircraft engine.
Description of Related Art
The use has hitherto been known of an IDG system (Integrated Drive Generator system), in which a continuously variable transmission is used for an electric generator used in a large scale aircraft so that the electric generator can be driven at a constant number of revolutions regardless of the number of revolutions of the engine to generate an electric power of a constant frequency. The generator device of the IDG system referred to above has also been known in which a traction continuously variable transmission, combined with a planetary gear transmission for compensating for the low mechanical efficiency of such traction continuously variable transmission, is provided with a constant speed drive device of a power split type for distributing and loading a power between those transmissions by means of a power splitting shaft. In this respect, see the patent document 1 listed below.
On the other hand, the aircraft engine of a two shaft type or double shaft type has been largely utilized in which are provided a hollow high pressure shaft, which is drivingly coupled with a compressor and a high pressure turbine, and a low pressure shaft, inserted in the hollow of the high pressure shaft and drivingly connecting between a fan and a low pressure turbine. In particular, since in the aircraft generating device equipped with the constant speed drive device of the power split type referred to previously, the planetary gear transmission operates at a fixed gear ratio, the gear ration of the constant speed drive device as a whole is limited to a value smaller than about 2:1. Accordingly, in the case of the double shaft system, an input shaft of the constant speed drive shaft is drivingly connected with the high pressure shaft that is small in change of the number of revolutions.
In the meantime, the output of the electric power generating device of the conventional IDG system has hitherto been about 90 kVA, but the aircrafts in recent years have come to require a large electric capacity exceeding 200 kVA consequent upon the increasing utilization of electricity in those aircrafts. Where such a large electric capacity generation takes place, and if the electric power generating device is connected with the high pressure shaft of the aircraft engine as hereinabove discussed, a problem (stall) occurs in the operation of the high pressure shaft system when the electrical load of the aircraft becomes considerable, and, therefore, the connection of the electric power generating device with the high pressure shaft is not desirable. In view of this, the air craft electric power generating device has been suggested of the type that is driven by the rotation transmission of the low pressure shaft having a no limitation in load to be extracted. In this respect, see the patent document 2 listed below.